U.S. Provisional Application No. 61/394,019, filed Oct. 18, 2010, is incorporated herein by reference in its entirety.
Bore finishing, which for the purposes here focuses on lapping which achieves super fine finishes, and also honing for fine finishes, typically utilizes an abrasive for removing material from the surface of a bore to achieve a desired bore size and finish on the bore surface. The manner of achieving bore finishing of concern utilizes a sleeve, referred to as a lapping sleeve for lapping, having a cylindrical or substantially cylindrical outer surface that acts on a workpiece bore with the abrasive. For honing the abrasive is fixed to the sleeve surface, and it will be desirable to have a means to adjust the diameter of the honing surface for achieving a certain bore size and to compensate for abrasive wear. For lapping, the abrasive is loose, in the form of a compound with a fluid carrier such as a paste. Because the abrasive is loose, it can be replenished or replaced, but will cause wear to the lap surface, and because of that and that the bore being lapped will increase in diameter during the lapping operation, it is desirable to have a means to adjust the diameter of the lapping sleeve.
Adjusting the diameter of the outer sleeve of a bore finishing tool such as a lapping sleeve is typically accomplished by having a tapered internal interface between the sleeve and an arbor or wedge received in the sleeve. In particular, an internal circumferential surface on the sleeve, is disposed about, and in mating relation to, a tapered outer surface on the arbor or wedge. The sleeve is cut or slit lengthwise, helically, or such so that it will expand diametrically when the sleeve is displaced axially relative to the arbor in the direction of divergence of the tapered surface of the arbor, that is toward the larger diameter end of the taper of the arbor.
The typical lapping sleeve, therefore, has a C-shaped cross section. The wall thickness of this section is necessarily larger at one end than the other, that is, at the converging end, due to the taper of the internal surface. The force required to expand the lap is the mathematical integration of the force required to open this C-shaped section over the entire length of the sleeve. It is easy to see that the greatest resistance to opening this sleeve (i.e. expanding it diametrically) is to be found at the end with the greatest wall thickness.
In most lapping operations, expansion of the lapping sleeve is done manually, often with a hammer blow to the thick-walled end of the sleeve. Such an impact is often necessary to overcome the significant force of opening the C-shaped cross section. Sometimes expansion is accomplished by means of screw thread on the lapping arbor which has the advantage of providing a more controlled force. But this force is typically applied slowly which can result in a small bulge in the lapping sleeve due to the high frictional forces between the sleeve and arbor. This bulge constitutes a degradation of the cylindricity of the lapping surface that can adversely affect the cylindricity of the bore being lapped. This deformation due to high expansion forces and friction can also be present when the sleeve is expanded by means of a hammer blow.
Very little has been done to change the basic design of slit-sleeved lapping tools that expand by means of mating with a tapered arbor or wedge. Reference, Largeteau U.S. Pat. Nos. 4,223,485 and 4,424,648 which describe a lapping sleeve that is made easier to expand while retaining a cylindrical outer surface by means of longitudinal slots cut through the wall. However, a disadvantage is that there is no single slot cut from one end of the sleeve to the other, and thus a multitude of such slots are required to give the sleeve expansion capability. At each slot some amount of lapping surface is lost, which in most lapping operations will result in a greater rate of tool wear. Furthermore, although most lapping operations generate very low amounts of torque between the sleeve and workpiece bore, some applications generate more torque even if only momentarily. Being cut all the way through in multiple locations, the sleeve would be ill-suited to resist any significant torque without the addition of some keyed features.
Lapping sleeves must also be periodically retracted, usually after one bore has been lapped and another of the same starting size must be lapped. Retraction is accomplished by applying the same large force to the sleeve but in the opposite direction. This force is applied at the end of the lapping sleeve, but at the thin-walled end of the sleeve. At this very thin cross section, a problem that can occur is that a force sufficient to retract the sleeve can cause high stresses, approaching or exceeding the yield point of the sleeve material. It has been observed that, after several applications of this retraction force, the sleeve may be visibly deformed in this location. In many cases this deformation will also degrade the cylindricity of the lapping sleeve and subsequently degrade the resulting cylindricity that can be achieved with the lapping tool.
As another disadvantage of known lapping tools for applications wherein cycle time and productivity is of concern, is that the known bore lapping tools require the lapping compound to be applied externally to the lapping surface, and time is required prior to commencement of the lapping operation, or during the process, to apply lapping compound.
Thus, what is sought is an improved sleeve type bore finishing tool, particularly for lapping or honing, that reduces the force to diametrically expand and retract the sleeve so as to be less likely to cause a permanent deformation thereof, and which overcomes one or more of the other shortcomings and disadvantages set forth above.